The purpose of this study is to evaluate the efficacy of Immunotherapy in asthmatic patients allergic to mite allergens. Study subjects will be selected from patients with a history of bronchial asthma whose symptoms are suggestive of mite sensitivity (perennial asthma symptoms aggravated by exposure to house dust). Patients will be evaluated for the presence of significant mite hypersensitivity by: (1) SKIN TEST: Prick method with mite extract using a standard technique will be utilized. Prick tests will also be performed, with a panel of nine common inhalant allergens to determine atopic status. Patients with positive skin test to mite will be skin prick tested to a positive end point (end point titration) with serial dilutions of the mite extract. (2) IN VITRO IgE and IgG ANTIBODIES: Total serum IgE levels, and mite specific IgE and IgG antibodies will be determined by the RAST and ELISA methods. (3) PROVOCATION INHALATION CHALLENGE: Patients with mite sensitivity will be challenged with methacholine (to determine degree of non-specific bronchial reactivity), followed by mite extracts (to assess specific mite reactivity). Thirty asthmatics with clinical laboratory evidence of mite hypersensitivity (Positive skin test and/or RAST, positive inhalation challenge to mite) will be selected for the study of immunotherapy to be performed in a double blind fashion with either mite extract or saline placebo control. Results of immunotherapy will be evaluated by daily symptom and medication scores (clinical course), periodic pulmonary function studies, IgE levels, specific anti-mite IgE and IgG antibody levels, and change in inhalation challenge response (PD20) to methacholine and mite extracts.